Heretofore there have been many different pressure controlled switch constructions proposed, and many of such switches have been controlled by the differential in pressure applied to two different areas of the switch, or its controls. Normally two areas or chambers in the switch each have a fluid inlet connection provided therefor whereby the differential in the pressures applied on opposite faces of a flexible control diaphragm will control switch opening and closing action. Or, the two pressures can be applied to an axially movable member, such as a piston for switch closing and opening action, depending upon the switch design and the pressure differentials available. This general type of a control switch has been used in many instances in braking systems to indicate when braking pressures are equalized or when they become out of balance, and the differential pressure switches or pressure actuated switches have been used in many instances in pressure steering applications. Representative patents in the field include patents such as U.S. Pat. Nos. 3,807,809 and 3,737,603.
In some instances, a switch closing action has been provided by distortable diaphragms in the switches and patents on this type of switch include U.S. Pat. Nos. 2,817,727 and 3,534,328.